Adjustable sliding brush transformer



United States Patent O M 3,537,051 ADJUSTABLE SLIDING BRUSH TRANSFORMER Henry J. Helberg and Robert J. Sziemkiewicz, Fort Wayne,

Ind., assignors to General Electric Company, a corporation of New York Filed Feb. 24, 1969, Ser. No. 801,663 Int. Cl. H01f 21/02 U.S. Cl. 336--148 9 Claims ABSTRACT OF THE DISCLOSURE An adjustable sliding brush transformer wherein a rotatable brush arm is secured to a shaft insulator and electrically connected to a stationary collector arm through a wave Washer maintained in compression between the brush arm and the collector arm by a snap ring which engages the collector arm and is received in a groove in the shaft insulator. A predetermined desired end play of the shaft with respect to the core and coil assembly is determined by the difference in width of a groove in the shaft and a snap ring received thereon,

BACKGROUND OF THE INVENTION This invention relates to adjustable sliding brush transformers and more particularly to construction features relating to the assembly of the sliding brush and its electrical connections to a core and coil assembly.

Adjustable sliding brush transformers generally include a single winding wound on a magnetic core, the winding being energized by a predetermined alternating current source. A sliding brush is provided to slide along a brush track formed on a surface of the single winding and to be connected to an output terminal. The sliding brush picks olf a voltage from the winding, which voltage varies with the brush position with respect to the winding. An example of this type of adjustable sliding brush transformer is disclosed for example in U.S. Pat. No. 2,009,013, Karplus et al. These transformers find use in various types of motor controls, power supplies and many other types of equipment.

In most adjustable sliding brush transformers the sliding brush is adapted to be rotated with respect to the core and coil assembly by rotation of a shaft which extends through the core and coil assembly coaxially therewith. Various mechanisms have been provided for causing the brush to be rotated by the shaft with respect to the core and coil assembly, while maintaining electrical connection between the brush and a terminal fixed on the core and coil assembly, and for supporting the shaft with respect to the core and coil assembly. In general, the better mechanisms from a performance standpoint have been quite complex, involving a considerable number of parts with attendant assembly problems, and very critical manufacturing tolerances. Conversely, the more simple mechanisms have not been the most satisfactory from a performance standpoint.

OBJECTS OF THE INVENTION It is therefore a primary object of this invention to provide a novel and improved construction, without critical manufacturing tolerances, in an adjustable sliding brush transformer for causing the brush to be rotated by a shaft with respect to the core and coil assembly while maintaining an electrical connection between the brush and a terminal fixed on the core and coil assembly, and for supporting the shaft with respect to the core and coil assembly.

It is another object of the invention to provide a novel and improved construction without critical manufacturing tolerances, for securing a brush supporting arm to,

3,537,051 Patented Oct. 27, 1970 ICC and insulating a brush supporting arm and a collector arm from an operating shaft in an adjustable sliding brush transformer, while maintaining an electrical connection between the rotatable brush supporting arm and the collector arm, one end of which is secured to the core and coil assembly.

It is still another object of the vinvention to provide a novel and improved construction in an adjustable sliding brush transformer wherein a desired end play of the operating shaft is automatically provided while assembly is greatly simplified.

It is a further object of this invention to provide anovel and improved construction of an adjustable sliding brush transformer which incorporates a minimum number of inexpensive parts which are readily assembled with minimal effort and skill. f

SUMMARY OF THE INVENTION The foregoing objects are accomplished in accordance with this invention when in a preferred embodiment a tube is supported coaxially within a core and coil assembly of an adjustable sliding brush transformer to journal a shaft, the rotation of which shaft is adapted to rotate a sliding brush. A shaft insulating member, having a head portion which forms a shoulder with a shank portion, is provided with a bore in the shank portion for receiving and being secured to one end of the shaft. A resilient electrically conductive brush supporting arm is provided with an aperture which receives the shank portion of the shaft insulating member such that the brush supporting arm may be secured to the head portion of the shaft insulating member against the shoulder. External electrical connection is made to the brush through the brush supporting arm and a collector arm, a first portion of which collector arm is secure to the core and coil assembly and a second portion of which is provided with an aperture for receiving the shank portion of the shaft insulation member. An electrically conductive spring means is positioned over the shank portion between the brush arm and the collector arm and is maintained in compression therebetween to provide an electrical connection between the arms by a retaining means which engages the collector arm and the shank portion of the shaft insulating member.

The shaft is retained in the tube by providing near a first end of the shaft a groove which receives a retaining member and by the shaft insulating member presstit on the other end of the shaft. The shaft insulating member is pressed onto the shaft until it engages one end of the tube while the retaining member engages the other end of the tube and the inner shoulder of the groove in the shaft. The groove is of a first predetermined width which is greater than the second predetermined width of the retaining member, such that when the assembly force applied to press-fit the shaft insulating member to the shaft is removed, a shaft end clearance equal to the difference between the first and second predetermined widths will be provided.v

BRIIEF DESCRIPTION OF THE DRAWING FIG. 1 is a circuit diagram of a typical adjustable sliding brush transformer;

FIG. 2 is a perspective view with a portion broken away of an adjustable sliding brush transformer embodying the novel and improved construction of this invention;

|FIG. 3 is an exploded perspective view showing several components of the adjustable sliding brush transformer shown in FIG. 2 prior to assembly;

lFIG. 4 is an enlarged side view of the adjustable sliding brush transformer shown in IFIG. 2 with portions broken away for sake of clarity; and

FIG. is an enlarged plan side view of the lower portion of the operating shaft as viewed in FIG. 3.

DESCRIPTION OP A PREFERRED EMBODIMENT The internal circuit arrangement of the adjustable sliding brush transformer of (FIG. 2 is shown in `FIG. l with the input terminals to the left and the output terminals to the right. The adjustable sliding brush transformer is provided with an auto-transformer coil 12, the ends of which are connected to terminals 14 and 16 for energization from an alternating current source (not shown). The coil 12 is adapted to be contacted by a sliding brush 18 which is connected to a terminal 20. Thus, a portion of the input voltage applied between terminals 14 and 16 is available as an output voltage between terminals 20 and 16. In order to provide an increase in the range of output voltages obtainable between the terminals 116 and 20', which range would include voltages even higher than the input voltage, a terminal 22 'is connected to an intermediate tap on the coil 12.

Referring now to FIG. 2, the novel and improved construction of the adjustable sliding brush transformer 10 contemplated by this invention will be described. The coil 12 of the adjustable transformer is Wound around an annular shell of insulating material 24 which encloses an annular magnetic core 26 of helically wound magnetic strip material formed as a toroidal core. The shell 24 comprises two portions 28 and 30 which are formed of a suitable insulating material such as phenolic resin or the like. Each portion includes inner 32 and outer 34 substantially cylindrical rims extending from a toroidal web portion 36. The winding 20 is formed by winding insulated wire around the shell 24 in successively disposed adjacent wire turns. As viewed in FIGS. 2 and 4, a portion of the wire insulation and possible some of the conductive metal is removed from the top surface of Vthe turns near the perimeter to form a brush track 38.

The terminals for making external input and output connections to the adjustable sliding brush transformer are provided by a terminal assembly l which is formed in part by projections 42 and 44 radially extending from the insulating shell portions 28 and 30 respectively. While the outer rim 34 of the shell is generally cylindrical, a flat portion 46 extending radially outward a slight clis-r tance from the cylindrical rim 34 is provided in the area of the terminal assembly 40` between the projections 42 and 44. A pair of rectangular grooves 48 and 50y are formed inthe projections 42 and 44 respectively for the purpose of providing a means for securing an insulating terminal board 52 over the -at portion 46.

As is best seen in FIG. 4, terminals 14, 16, and 22 are formed as U-shaped members with the legs being received in rectangular apertures in the terminal board 52 such that a portion of the terminal board rests in the bight of the U-shaped members. The other leg of each U-shaped member is formed with a notch Within which a lead from the coil 12 is wound and soldered. A lead 54 which is soldered to the other leg of terminal 22 is brought out as a tap from one of the turns of the coil 12. Similarly, lead 56 from one end of the coil 12 is soldered to terminal 14, and lead 58 from the other end of coil 12 is soldered to terminal 16.

With the U-shaped terminals 14, 16, and 22 positioned in the apertures in the insulating terminal board 52, the board is moved from either side into position overlying the flat portion 46 formed on the shell portions 28 and 30. The upper end of the terminal board 52 is received within the groove 48, and the lower end is received within the groove 50. With the terminal board 52 positioned over the fiat portion 46, the U-shaped terminals 14, 16, and 22 are captured and secured in position.

Terminal 20, through which external connections are made to the sliding brush 18, is as an extension of a co1- tion 36 and in the projections 42 and 44 respectively. As

is best seen in FIG. 2, the groove 68 is of substantially the same width as the collector arm 60, such that when collector arm 60 is secured by screw 62, the groove 68 substantially captures and prevents rotation of the collector arm 60. A pair of pockets 72 and 74 are formed on the inside surfaces of the projections 42 and 44 respectively for receiving a nut 76 which is threadedly engaged by the screw 62. The side walls of the pockets 72 and 74 substantially conform to the shape of the nut 76, which is shown as hexagonal, and the height of the pockets 72 and 74 conform to the thickness of the nut 76, such that the nut 76 is captivated within the pocket 72 and prevented from turning therein when threadedly engaged by the screw 62.

While the manner in which the collector arm 60 is secured to the shell portion 28 has been described in connection with an overall description of the terminal assembly 40, it is not secured thereto until it is first included in a sub-assembly, which sub-assembly is best described by making reference to FIGS. 3 and 4. The sliding brush 18 which contacts the brush track 38 is received within a rectangular pocket 78 formed in a resilient electrically conductive brush arm 80. As depicted in FIG. 4, an operating knob 82 secured to a shaft 84 by a set screw 86 is utilized to rotate the brush arm and therefore sliding brush 18 on the brush track 38. While it is necessary to provide a positive electrical connection between the collector arm 60 and the brush arm 80, it is also highly desirable to provide electrical insulation between these arms and the shaft 84, such that the shaft will not be maintained at the potential appearing at the sliding brush 18. These objectives are accomplished by providing a shaft insulating member 88 which is provided with a cylindrical bore 90 therein for receiving in frictional engagement a reduced diameter knurled portion 92 of the shaft 84. The shaft insulator 88 is formed with a head portion 94 which forms shoulder 96 with a cylindrical shank portion 98.

To facilitate the assembly of the brush arm 80 and the collector arm 60 to the shaft insulator 88, a pair of diametrically opposed notches 100 are formed in the head 94, and an annular groove 102 is formed in the shank 98. The brush arm 80 is provided with an aperture 104 having substantially the same diameter as shank 98 of the shaft insulator 88 and is received thereover to rest against the shoulder 96. Brush arm 80 is provided with a pair of tabs 106 and 108 adjacent the aperture 104 which tabs are formed over the shaft insulator 88 into the notches 96 and 100 respectively to secure the brush arm 80 to the shaft insulator 88. The collector arm 60, like the brush arm 80, is provided with an aperture 110 therein which is designed to loosely fit over the shank 98 of shaft insulator 88.

In order to provide the desired positive electrical connection between the brush arm 80 and the collector arm 60, which arms rotate with respect to each, an electrically conductive spring means such as wave Washer 112 is interposed therebetween. In assembling the collector arm 60 and the brush arm 80 to the shaft insulator 88, a pressure is exerted between the collector arm 60 and the shaft insulator 88 to atten the wave washer 112. The compressive force on the wave Washer 112 is maintained by a retaining member, such as snap ring 114 which is received in the groove 102 in the shank portion of shaft insulator 88. Release of the assembly pressure between the collector arm 60 and the shaft insulator 88 will permit the Wave f washer 112 to press the collector arm 60 against an abutting surface of snap ring 114, while maintaining an expansive force and electrical contact between the brush arm 80 and the collector arm 60.

With the sub-assembly of the collector arm 60, brush arm 80, and shaft insulator 88 completed, the further assembly of this sub-assembly and of the shaft 84 and other members supporting the shaft upon the core and coil subassembly is now possible. Referring to FIGS. 2 and 4, at the bottom of the core and coil assembly will be seen a circular sheet metal member 116 having a raised central portion 118, which sheet metal member 116 is provided to protect the lower end of the core and coil assembly and is insulated therefrom by a cylindrical insulating member 120. Similarly, at the top of the core and coil assembly a cup-shaped sheet metal member 122 is placed over the central aperture of the core and coil assembly. The cup-shaped member 122 has a at bottom portion 124 and a flared top portion 126 which engages the inner edge of the top of the core and coil assembly. 'I'he cupshaped sheet metal member 122 is shown entirely coated with an insulating material 128 to forego any chance of cup-'shaped member 122 providing a short between turns of the coil 12 should the insulation on the coil be inadequate for any reason, but also more importantly to provide insulation between the tube 130 and the coil 12. This insulation could also be provided by an insulating member provided between cup-shaped member 122 and coil 12 in a manner similar to that of cylindrical insulating member 120.

With the sheet metal member 116 in position at the bottom of the core and coil assembly and the cup-shaped member 122 in position at the top of the core and coil assembly, a tube 130 is inserted through apertures 132 and 134 provided in cup-shaped member 122 and sheet metal member 116 respectively to provide a supporting passageway for the shaft 84. It will be noted in FIG. 4 that a retaining washer 136 which is received in a groove provided close to the upper end of the tube 130` engages the upper surface of the fiat bottom portion 124 of the cup-shaped member 122. In an alternative arrangement a head could be provided at the upper end of the tube 130 in place of the retaining washer 136. The lower end of the tube 130 is provided with threads 138 such that after a washer 140 is placed over the sheet metal member 116, a nut 142 may be threaded onto the tube to provide a clamping force through the tube 130 between the cupshaped member 122 and the sheet metal member 116 to secure these members and the tube 130 to the core and coil assembly.

With the tube 130 secured to the core and coil assembly, the assembly of the adjustable sliding brush transformer may now be completed by the installation of the shaft 84 within the tube 130 and the securing of the shaft insulator 88 to the shaft. As best seen in FIG. 5, a retaining member shown as snap ring 144 is first secured in an annular groove 146 formed in the shaft 84. With the, snap ring 144 in place on the shaft 84, the shaft is inserted through the lower end of the tube 130, as viewed in FIGS. 2 and 4, until the snap ring 144 engages the lower end of the tube 130. With a force applied to the lower surface of snap ring 144 so as to maintain contact between the upper surface of snap ring 1-44 and the lower end of the tube 130, the shaft insulator 88 is pressed on the top end of the shaft to be frictionally retained on the shaft by the engagement of the knurled portion 92 of the shaft within the cylindrical bore 90 of the shaft insulator 88. The shaft insulator 88 is pressed onto the shaft until lower end 148 of the shaft insulator engages upper end 150 of the tube 130.

Referring to FIG. 4, it will be seen that the knurled portion 92 of the shaft 84 is formed on a reduced diameter portion 152 of the shaft. Wherein the reduced diameter portion 152 of the shaft 84 continues a distance lbelow the upper end 150 of the tube 130, and wherein the cylindrical bore 90 in the shaft insulator 88 is of sumcient depth, insertion of the knurled portion `92 into the bore of the shaft insulator 88 is limited only by engagement of the lower end 148 of the shaft insulator 82 with the upper end 150 of the tube.

By making further reference to FIGS. 4 and 5 and particularly FIG. 5, it will be seen that the assembly of the shaft insulator 88 to the shaft 84 automatically provides a desired amount of end play of the shaft 84 with respect to the tube and core and coil assembly. The groove 146 in the shaft 84 is formed with a greater width than that of the snap ring 144 received therein. As the pressure is applied to the top of the shaft 84 by pressing the shaft insulator 88 thereon, the top surface of the snap ring 144 will be pressed against top edge or inner shoulder 154 of groove 146. When the lower end 148 of the shaft insulator 88 engages the upper end 150 of the tube 130, the distance between the lower end 148 of the shaft insulator 88 and the inner shoulder 154 of the groove 146 will be exactly the predetermined overall length of the tube 130. When the force of assembling the shaft insulator 88 to the shaft 84 is removed, the snap ring 144 will back off to a position in engagement with the lower end or outer shoulder 156 of groove 146 as shown in FIG. 5. Thus, end play of the amount indicated by the dimension C in FIG. 5 is provided. This end play is substantially equal to the difference in dimensions of the width of the groove 146 and the thickness of the snap ring 144.

While the manner of assembling the adjustable slidin-g brush transformer has proceeded With reference being made to the principal features of interest, it should be noted that when the shaft insulator 88 is positioned to be pressed onto the shaft 84, the collector arm 60 is positioned within the groove 68 such that it may be secured to the shell portion 28 by the screw 62 and the nut 76 as previously set forth. It should also be observed that the brush 18 is formed with a pair of shoulders 158 and 160 and an upwardly projecting portion 162 therebetween, such that the shoulders engage folded portion 164 of the brush arm, and the projecting portion 162 is received within the pocket 78. The brush arm 80 is so formed and so assembled that it exerts a downward spring force on the brush 18 to force the brush against the brush track 38. Also, the collector arm 60 is provided with a pair of upstanding tabs 166 and 168 which serve as stops for the rotation of brush arm 80.

Referring to FIG. 4, the threaded portion 138 of the tube 130 is made sufficiently long such that it may be inserted through an aperture formed in a plate or` panel 170 upon which the adjustable sliding brush transformer 10 is to be mounted and be secured thereto bythe clamping force of a second nut 172 threaded onto the threaded portion 138 of the tube 130. It is frequently desirable to provide an indicating dial on the face of the panel, and such a dial 174 may be placed on the panel underneath the nut 172 and a washer 176. Finally, the installa tion of the adjustable transformer 10 is completed by securing operating knob 82 to the shaft 84 by set screw 86.

While a particular embodiment of this invention has been shown and described, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from this invention in its broader aspects and, therefore, it is intended that the appended claims cover all such changes and modifications as fall within the true spirit and scope of this invention.

What we claim as new and desired to secure by Letters Patent of the United States is:

1. In an adjustable sliding brush transformer having an annular magnetic core formed of a strip of magnetic material Wound with a central opening, a shell of insulating material having inner and outer substantially cylindrical rims extending between toroidal web portions disposed on said annular core, a winding of successively disposed adjacent wire turns wound on the shell and overlying the annular core to form a core and coil assembly, a brush track formed on the turns over one of the web portions at one end of the core and coil assembly, a pair of members, one at each end of the core and coil assembly, for supporting a tube in the central opening of the core and coil assembly substantially coaxially therewith, the invention compirsing:

(a) a shaft extending through the bore of the tube,

and rotatable therein,

(b) a shaft insulator having a head portion and a cylindrical shank portion, said head portion forming a shoulder with said shank portion, said shank portion being provided with a bore therein for receiving oneend of said shaft, which end of said shaft is secured to said shank portion, said cylindrical shank portion being provided with an annular groove spaced a predetermined distance from said shoulder,

(c) a resilient electrically conductive brush supporting arm having an aperture formed therein for receiving the shank portion of the shaft insulator, said brush arm being provided with at least one tab adjacent said aperture for securing said brush arm against said shoulder to said head portion of said shaft insulator, such that said brush arm is rotatable by said shaft,

(d) an electrically conductive collector arm, a first portion of said collector arm secured to said core and coil assembly, a second portion of said collector arm having an aperture formed therein for receiving the shank portion of said shaft insulator,

(e) an electrically conductive spring means received over the shank portion of the shaft insulator, and interposed between said brush arm and said current collector arm,

(f) a retaining member received in said groove in said shaft insulator, said retaining member engaging said collector arrn and said brush arm engaging said shoulder, and said conductive spring means being compressed between said brush arm and said current collector arm to maintain a constant electrical connection therebetween, whereby external electrical connection may be made to the brush supported by said brush arm through said brush arm, said spring means and said collector arm.

2. The adjustable sliding brush transformer defined in claim 1 wherein said head portion of said shaft insulator is provided with at least one notch therein for receiving said tab of said brush arm to secure said brush arm against said shoulder and to assure rotation of said brush arm with said shaft insulator.

3. The adjustable sliding brush transformer defined in claim 1 wherein said spring means is a wave washer and said first retaining member is a snap ring.

4. The adjustable sliding brush transformer defined in claim 1 wherein a first portion of the outer substantially cylindrical rim is formed to have mounted thereon a terminal board, the invention comprising: a projection radially extending from the first portion of the outer substantially cylindrical rim, adjacent the web portion at the one end of the core and coil assembly, said projection being provided with a pocket therein, and said projection being provided with an aperture passing axially through the projection and into said pocket, said collector arm being provided with a second aperture which is aligned with said aperture in said projection, a screw received in said aperture, and a nut received in said pocket for engagement with said screw, said pocket being formed to prevent rotation of said nut, whereby said screw is threaded into said nut to secure said collector arm to said core and coil assembly.

5. In an adjustable sliding brush transformer having an annular magnetic core formed of a strip of magnetic material wound with a central opening, a shell of insulating material having inner and outer substantially cylindrical rims extending between toroidal web portions disposed on said annular core, a winding of successively disposed adjacent wire turns wound on the shell and overlying the annular core to form a core and coil assembly, a brush track formed on said turns over one of the web portions at one end of the core and coil assembly, a pair of members, one at each end of the core and coil assembly, for supporting a tube of a predetermined length in the central opening of the core and coil assembly substantially coaxially therewith, the invention comprising:

(a) a shaft extending through the bore of the tube, said shaft being provided near a first end with an annular groove of a first predetermined Width, said groove forming an outer shoulder adjacent the first end of said shaft and an inner shoulder toward the other end of said shaft,

(b) a shaft insulator having a head portion and a cylindrical shank portion, said head portion forming a shoulder with said shank portion, said shank portion being provided with a bore therein for receiving the other end of said shaft in a press-fit relationship,

(c) a resilient electrically conductive brush supporting arm having an aperture formed therein for receiving the shank portion of the shaft insulator, said brush arm being secured against said shoulder to said head portion of said shaft insulator,

(d) an electrically conductive collector arm having an aperture formed therein for receiving the shank portion of said shaft insulator,

(e) an electrically conductive spring means received over the shank portion of the shaft insulator, and positioned between said brush arm and said current collector arm,

(f) a retaining means cooperating with said shank portion of said shaft insulator and said collector arm, and said brush arm engaging said shoulder, such that said conductive spring means is compressed between said brush arm and said current collector arm to maintain a constant electrical connection therebetween,

(g) a retaining member of a second predetermined width which is lesser than said first predetermined width of said annular groove in said shaft, said shaft insulator being press-tit on said shaft such that the distance between said inner shoulder of said groove in said shaft and the end of the cylindrical shank portion of said shaft insulator is the same as the predetermined length of the tube, whereby with said retaining member engaging the outer shoulder of said groove in said shaft, a desired end play of said shaft is provided, which is equal to the difference between the first predetermined width of said groove in said shaft and the second predetermined width of said retaining member.

6. The adjustable sliding brush transformer defined in claim 5 wherein said cylindrical shank portion is provided with an annular groove spaced a predetermined distance from said shoulder, said retaining means being received in said groove in said shaft insulator and engaging said collector arm, said brush arm engaging said shoulder such that said conductive spring means is compressed between said brush arm and said current collector arm to maintain a constant electrical connection therebetween.

7. The adjustable sliding brush transformer defined in claim 5 wherein said brush arm is provided with at least one tab adjacent said aperture therein, and said head portion of said shaft insulator is provided with at least one notch therein for receiving said tab of said brush arm to secure said brush arm against said shoulder and to assure rotation of said brush arm with said shaft insulator.

8. The adjustable sliding brush transformer defined in claim 5 wherein said spring means is a waive washer and said retaining means and said retaining member are snap rings.

9. The adjustable sliding brush transformer defined in claim 5 wherein a first portion of the outer substantially cylindrical rim is formed to have mounted thereon a terminal board, the invention comprising: a projection radially extending from the iirst portion of the outer substantially cylindrical rim, adjacent the web portion at the one end of the core and coil assembly, said projection being provided with a pocket therein, and said projection being provided with an aperture passing axially through the projection and into said pocket, said collector arm being provided with a second aperture which is aligned with said aperture in said projection, a screw received in said aperture, and a nut received in said pocket for engagement with said screw, said pocket being formed to prevent rotation of said nut, whereby said screw is threaded into said nut to secure said collector arm to said core and coil assembly.

References Cited UNITED STATES PATENTS U.S. Cl. X.R. 

